U.S. patent number 7,875,155 [Application Number 12/280,993] was granted by the patent office on 2011-01-25 for transparent electrically conductive film and method for production thereof.
This patent grant is currently assigned to Sumitomo Chemical Company, Limited. Invention is credited to Akira Hasegawa, Takeshi Hattori, Yuzo Shigesato.
United States Patent |
7,875,155 |
Hattori , et al. |
January 25, 2011 |
Transparent electrically conductive film and method for production
thereof
Abstract
The present invention provides a transparent electrically
conductive film and a method for producing the same. The
transparent electrically conductive film comprises Zn, Sn and O,
wherein the molar ratio Zn/(Zn+Sn) of Zn to the sum of Zn and Sn is
0.41 to 0.55, and is amorphous.
Inventors: |
Hattori; Takeshi (Chiba,
JP), Hasegawa; Akira (Ibaraki, JP),
Shigesato; Yuzo (Kanagawa, JP) |
Assignee: |
Sumitomo Chemical Company,
Limited (Tokyo, JP)
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Family
ID: |
38594424 |
Appl.
No.: |
12/280,993 |
Filed: |
March 15, 2007 |
PCT
Filed: |
March 15, 2007 |
PCT No.: |
PCT/JP2007/055935 |
371(c)(1),(2),(4) Date: |
August 28, 2008 |
PCT
Pub. No.: |
WO2007/119497 |
PCT
Pub. Date: |
October 25, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090065746 A1 |
Mar 12, 2009 |
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Foreign Application Priority Data
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Mar 16, 2006 [JP] |
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2006-072569 |
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Current U.S.
Class: |
204/192.15;
252/519.51 |
Current CPC
Class: |
C23C
14/3414 (20130101); C01G 19/02 (20130101); C23C
14/086 (20130101); C01G 19/00 (20130101); C01G
9/02 (20130101); C01P 2004/03 (20130101); C01P
2006/40 (20130101) |
Current International
Class: |
H01B
1/08 (20060101); C23C 14/58 (20060101) |
Field of
Search: |
;252/519.5,519.51,520.1
;204/192.15 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1558962 |
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Dec 2004 |
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CN |
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101076869 |
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Nov 2007 |
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CN |
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60-68508 |
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Apr 1985 |
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JP |
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2004-022268 |
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Jan 1994 |
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JP |
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6-290641 |
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Oct 1994 |
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JP |
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08-171824 |
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Jul 1996 |
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JP |
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9-035535 |
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Feb 1997 |
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JP |
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09-35535 |
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Feb 1997 |
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JP |
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9-286070 |
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Nov 1997 |
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JP |
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2000-256061 |
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Sep 2000 |
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JP |
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2004-22268 |
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Jan 2004 |
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JP |
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2006-194926 |
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Jul 2006 |
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JP |
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2006-196200 |
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Jul 2006 |
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JP |
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2006-196201 |
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Jul 2006 |
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JP |
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2007-314364 |
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Dec 2007 |
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JP |
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2008/084865 |
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Jul 2008 |
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WO |
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2008/114850 |
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Sep 2008 |
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WO |
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Other References
Minami et al "Highly Transparent and Conductive Zinc-Stannate Thin
Films . . . ", Jap. J. Appl. Phys. vol. 33(1994) pp. L1693-L1696.
cited by examiner .
Moriga et al "Transparent conducting amorphous Zn-Sn0O films
deposited by simultaneous dc sputtering", J. Vac. Sci. Technol.
A.22(4) Jul./Aug. 2004 pp. 1705-1710. cited by examiner .
T Minami et al.; Properties of transparent zinc-stannate conducting
films prepared radio frequency magnetron sputtering; J. Vac. Sci.
Technol. A; 13(3); May/Jun. 1995, pp. 1095-1099. cited by other
.
Minami et al.; Highly Transparent and Conductive Zinc-Stannate Thin
Films Perpared RF Magentron Sputtering; Appl. Phys. vol. 33 (1994);
Dec. 1, 1994 pp. L 1693-L 1696. cited by other .
U.S. Appl. No. 12/522,383, filed Jul. 8, 2009, corresponding to WO
2008/084865. cited by other.
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Primary Examiner: Kopec; Mark
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
The invention claimed is:
1. A method for producing a transparent electrically conductive
film, the method comprising a step of sputtering under an inert gas
atmosphere, using as a target a sintered body comprising Zn, Sn and
O wherein the molar ratio Zn/(Zn+Sn) of Zn to the sum of Zn and Sn
is 0.53 to 0.65, further comprising a step of thermally treating a
transparent electrically conductive film under a reducing gas
atmosphere at 300.degree. C. to 500.degree. C., wherein the
reducing gas comprises 2 to 4 wt% of hydrogen and 98 to 96 wt % of
an inert gas.
Description
TECHNICAL FIELD
The present invention relates to a transparent electrically
conductive film and a method for producing the same.
BACKGROUND ART
Transparent electrically conductive films are used as an electrode
of displays such as a liquid crystal display, organic EL display
and plasma display, or an electrode of solar batteries. The
transparent electrically conductive film is required to have
sufficient conductivity, and from the standpoint of formation of an
electrode pattern, required to have also excellent etching
property. Conventionally, there are various suggestions on the
transparent electrically conductive film (for example, JP-A No.
8-171824).
Recently, with increase in the size of displays, improvements in
conductivity and etching property are desired also for transparent
electrically conductive films to be used as an electrode.
DISCLOSURE OF THE INVENTION
The present invention has an object of providing a transparent
electrically conductive film excellent in conductivity and etching
property, and a method for producing the same.
The present inventors have intensively studied to solve the
problem, resultantly leading to completion of the present
invention.
That is, the present invention provides a transparent electrically
conductive film comprising Zn, Sn and O, wherein the molar ratio
Zn/(Zn+Sn) of Zn to the sum of Zn and Sn is 0.41 to 0.55, and is
amorphous.
Further, the present invention provides a method for producing a
transparent electrically conductive film, comprising a step of
sputtering under an inert gas atmosphere, a sintered body target
comprising Zn, Sn and O, wherein the molar ratio Zn/(Zn+Sn) of Zn
to the sum of Zn and Sn is 0.53 to 0.65.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an electron micrograph of a calcined material in Example
1.
MODE OF CARRYING OUT THE INVENTION
Transparent Electrically Conductive Film
The transparent electrically conductive film of the present
invention includes zinc (Zn), tin (Sn) and oxygen (O), and is
usually composed of a metal oxide containing Zn, Sn and O.
The ratio Zn/(Zn+Sn) of the amount (mol) of Zn to the total amount
(mol) of Zn and Sn contained in the transparent electrically
conductive film is not less than 0.41 and not more than 0.55, and
from the standpoint of improvement in etching property, preferably
not less than 0.42, further preferably not less than 0.43 and
preferably not more than 0.50, further preferably not more than
0.48.
The transparent electrically conductive film is amorphous.
Measurement may be advantageously carried out by X-ray
diffractometry, and in the instant specification, amorphous means
that, for example, in an X-ray diffraction pattern, a diffraction
peak derived from crystal is not detected.
The transparent electrically conductive film has a resistivity of
usually less than 1.times.10.sup.-2 .OMEGA.cm, preferably not more
than 7.times.10.sup.-3 .OMEGA.cm. The resistivity may be
advantageously measured by a four-point probe method. The
transparent electrically conductive film contains or does not
contain aluminum (Al), gallium (Ga) or indium (In), and those not
containing them are preferable.
Method for Producing Transparent Electrically Conductive Film
The method for producing a transparent electrically conductive film
of the present invention includes a step of sputtering a sintered
body used for a target.
The sintered body includes zinc (Zn), tin (Sn) and oxygen (O), and
is usually composed of a metal oxide containing Zn, Sn and O.
The ratio Zn/(Zn+Sn) of the amount (mol) of Zn to the total amount
(mol) of Zn and Sn contained in the sintered body is not less than
0.53 and not more than 0.65.
The sintered body may be advantageously prepared by a method of,
for example, mixing (grinding) zinc oxide and tin oxide, molding
the mixture, and sintering the resultant.
Zinc oxide is usually in the form of powder, and has a purity of
not less than 99 wt %. Tin oxide is usually in the form of powder,
and has a purity of not less than 99 wt %.
In mixing, zinc oxide and tin oxide are so weighed as to satisfy
that the ratio Zn/(Zn+Sn) of the amount (mol) of Zn to the total
amount (mol) of Zn and Sn contained in the mixture is not less than
0.53, preferably not less than 0.54 and not more than 0.65,
preferably not more than 0.61. For example, when a transparent
electrically conductive film having a Zn/(Zn+Sn) of not less than
0.41 and not more than 0.55 is produced, zinc oxide and tin oxide
may be advantageously so weighed as to satisfy that Zn/(Zn+Sn) is
not less than 0.53 and not more than 0.65. When a transparent
electrically conductive film having a Zn/(Zn+Sn) of not less than
0.42 and not more than 0.50 is produced, zinc oxide and tin oxide
may be advantageously so weighed as to satisfy that Zn/(Zn+Sn) is
not less than 0.54 and not more than 0.61. Mixing may be
advantageously carried out, for example, by using a ball mill,
vibration mill, attritor, Dyno mill or dynamic mill, and may be
carried out in dry or wet condition. From the standpoint of
improving operability in molding described later, tin oxide,
binder, dispersant or lubricant may be added to the mixture. When
mixing is carried out in wet condition, the resultant mixture may
be dried, and drying may be advantageously carried out, for
example, by using a heating dryer, vacuum dryer or freeze
dryer.
The mixture may be calcined, and calcination may be advantageously
carried out under conditions of keeping at temperatures lower than
sintering described later. When the mixture is calcined, it is
preferable that a binder, dispersant or lubricant are added to the
calcined mixture.
Molding may be advantageously carried out using, for example, a
mono-axial press or cold isostatic press (CIP) under condition of a
molding pressure of usually 10 to 300 MPa. A green body preferably
has a shape such as circular disc and square plate, suitable for
sputtering. In molding, operations for adjusting dimension such as
cutting and grinding may be combined. Sintering may be
advantageously carried out by, for example, maintaining a green
body under an oxygen-containing atmosphere (for example, air),
under conditions of a highest achievement temperature of not lower
than 900.degree. C. and not higher than 1700.degree. C. and a
retention time of 0.5 to 48 hours. Sintering may be advantageously
carried out by using an electric furnace or gas furnace. Molding
and sintering may be effected simultaneously using a hot press or
hot isostatic press (HIP). The resultant sintered body may be cut
or ground, to adjust dimension.
Sputtering is carried out under an inert gas atmosphere. Examples
of the inert gas include argon (Ar). It is preferable that the
atmosphere has an inert gas concentration of not less than 99.995%,
and contains substantially no oxygen. The oxygen concentration is
usually less than 0.05%. Sputtering may be advantageously carried
out by, for example, using a radio frequency magnetron sputtering
apparatus (rf magnetron sputtering apparatus), under conditions of
a radio frequency input power of 100 W to 300 W, an atmospheric
pressure of 0.1 Pa to 1 Pa, an atmosphere of Ar gas (using Ar gas
cylinder), and a temperature of object (for example, substrate) of
room temperature (25.degree. C.) to 300.degree. C.
The resultant transparent electrically conductive film may be
thermally treated under a reducing gas containing atmosphere at not
lower than 300.degree. C., preferably not lower than 350.degree. C.
and not higher than 500.degree. C., preferably not higher than
450.degree. C. By thermal treatment, a transparent electrically
conductive film having further lower resistivity is obtained.
Examples of the reducing gas include a mixed gas having a hydrogen
concentration of 2 to 4 wt % and an inert gas concentration of 98
to 96 wt %.
EXAMPLES
Example 1
Preparation of Sintered Body
A zinc oxide powder (ZnO, manufactured by Wako Pure Chemical
Industries, Ltd., guaranteed reagent) and a tin oxide powder
(SnO.sub.2, manufactured by Roj undo Chemical Laboratory Co., Ltd.,
purity: 99.99%) were weighed so that Zn/(Zn+Sn) was 0.55, and these
powders and ethanol were charged into a wet ball mill (medium:
zirconia ball with a diameter of 5 mm) and mixed, to obtain a
slurry. The slurry was dried with heating to remove ethanol,
obtaining a mixture. The mixture was charged into an alumina
crucible, and calcined under an air atmosphere at 900.degree. C.
for 5 hours. The calcined product and ethanol were charged into a
wet ball mill (medium: zirconia ball having a diameter of 5 mm) and
ground, to obtain a slurry. The slurry was dried with heating to
remove ethanol. The resultant dried product was dispersed in
ethanol, and polyvinyl butyral (manufactured by Sekisui Chemical
Co., Ltd., trade name: S-LEC B) was added as a binder, and these
were stirred, then, dried to obtain a powder. The powder was
charged into dies, and molded using a mono-axial press under
condition of a molding pressure of 30 Mpa, to obtain a green body
in the form of circular disc. The green body was sintered in air of
normal pressure (1 atm) at 1000.degree. C. for 5 hours, to obtain a
sintered body.
Production of Transparent Electrically Conductive Film
The sintered body and a glass substrate were set as a sputtering
target and as a film forming substrate, respectively, in a
sputtering apparatus (manufactured by ANELVA Corporation,
L-332S-FHS special type).
An Ar gas (purity: not less than 99.9995%, manufactured by Japan
Fine Products Corporation, "Ar pure gas-5N") was introduced into
the sputtering apparatus, and sputtering was carried out under
conditions of a pressure of 0.5 Pa, an electric power of 100 W and
a substrate temperature of 300.degree. C., to form a film on the
substrate. The film was analyzed using Auger electron spectroscopy
to determine the composition (Zn:Sn). Zn:Sn was 43.4 mol:56.6 mol.
The film had a resistivity of 7.times.10.sup.-3 .OMEGA.cm and a
carrier concentration of 2.times.10.sup.19, and was transparent to
visible light. The film was analyzed using X-ray diffractometry to
determine crystallinity thereof. The film was amorphous. Further,
the film was excellent in flatness and homogeneity.
Example 2
The transparent electrically conductive film formed in Example 1
was thermally treated under an Ar gas atmosphere containing 3 wt %
of H.sub.2 at 400.degree. C. The resultant film had a resistivity
of 5.times.10.sup.-3 .OMEGA.cm and was transparent.
Comparative Example 1
A film was formed in the same operation as in Example 1 excepting
that the ratio Zn/(Zn+Sn) of a zinc oxide powder and a tin oxide
powder was changed to 0.50 from 0.55 in [Preparation of sintered
body]. The film had Zn: Sn of 38.9 mol: 61.1 mol and a resistivity
of 1.times.10.sup.-2 .OMEGA.cm and was transparent.
Comparative Example 2
A film was formed in the same operation as in Example 1 excepting
that the ratio Zn/(Zn+Sn) of a zinc oxide powder and a tin oxide
powder was changed to 0.67 from 0.55 in [Preparation of sintered
body]. The film had Zn:Sn of 57.8 mol:42.2 mol and a resistivity of
1 .OMEGA.cm.
Industrial Applicability
The transparent electrically conductive film of the present
invention has low resistivity, that is, excellent in electric
conductivity. Further, the transparent electrically conductive film
is etched by, for example, a weak acidic oxalic acid aqueous
solution (oxalic acid concentration: 2 mol/liter) and excellent in
etching property. The transparent electrically conductive film is
suitably used as an electrode of displays such as a liquid crystal
display, organic EL display, flexible display and plasma display,
or an electrode of solar batteries. Further, the transparent
electrically conductive film is used also as infrared reflective
film for windowpane, an antistatic film or the like.
* * * * *